The principal aims of this project are to examine in greater detail the highly interdependent relationships between those factors which regulate intracellular sodium activity and net sodium transport and the transport systems for hydrogen and potassium ions. Isolated perfused proximal convoluted and proximal straight tubule segments from the superficial cortex will be compared with regard to transport and cell regulatory functions. The specific aims of the proposed experiments are to: 1) examine the effect of extracellular and intracellular pH on anion and cation perm-selectivity of the luminal and basolateral membranes 2) investigate the underlying mechanisms which result in the difference in apparent bicarbonate conductance of the basolateral membrane between the proximal convoluted and proximal straight tubule 3) examine the phenomenon of electrical potential oscillations in convoluted tubules with respect to the interaction between transport and cellular regulation of pH and 4) investigate the regulation of cellular potassium with particular emphasis on the luminal membrane. Measurements will be made with conventional microelectrodes and with double barreled ion selective electrodes for sodium, potassium, chloride, and hydrogen. The long term goals are to elucidate the basic mechanisms by which cellular ion exchanges and renal transport processes maintain homeostatic control of electrolyte and water balance of the body fluids.